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Eelgrass restoration in theDutch Wadden SeaResults 2014

Eelgrass restoration in the DutchWadden SeaResults 2014

1203892-000

© Deltares, 2014, B

dr. L.A. van Duren

DeltoresTitleEelgrass restoration in the Dutch Wadden Sea

ClientRWS-WVL

Project1203892-000

Reference Pages1203892-000-ZKS-0044 16

KeywordsEelgrass, seagrass, Zostera marina, restoration, Wadden Sea, Water Framework Directive

SummaryBefore ca. 1930, Eelgrass (Zostera marina) was widespread throughout the whole of theWadden Sea. Infrastructural works, disease, eutrophication and other factors havecontributed to its demise. In the Dutch Wadden Sea Eelgrass has virtually disappeared.Within the European Water Framework Directive targets are set to increase its occurrence.This report is an update with the 2014 monitoring data of the 2011 and 2012 deployments inthe Dutch Wadden Sea. At all three locations the Eelgrass population has decreasedsubstantially compared to the 2013 distribution. This is likely due to the diminished seeddevelopment observed in 2013. The results so far indicate that although there appears to besufficient suitable substrate in the Dutch Wadden Sea, seed supply is restrictive for thenatural recovery of the species. The restoration efforts within this project have probably beeninsufficiently large to ensure the long-term re-establishment of the species in the Dutch part ofthe Wadden Sea

drs.F.M.J.Hoozemans

Version Date Author Initials Review ti Initials A roval.nov.2014 dr. LA van Dure drs. J.A. van

Dalfsen

Statefinal

Eelgrass restoration in the Dutch Wadden Sea - Results 2014

1203892-000-ZKS-0044, 27 November 2014, final

Eelgrass restoration in the Dutch Wadden Sea - Results 2014 i

Contents

1 Background 11.1 Project background 11.2 Project outline 1

2 Deployment locations (2011 and 2012) 22.1 Uithuizen 22.2 Balgzand 22.3 Schiermonnikoog 2

3 Data collection on Eelgrass distribution 33.1 Annual monitoring in the vicinity 33.2 Eelgrass observations reported by the public via the RWS website 3

4 Monitoring observations at deployment locations 44.1 Uithuizen 4

4.1.1 Cover 44.1.2 Vitality and seed development 5

4.2 Balgzand 64.2.1 Cover 64.2.2 Vitality and seed development 8

4.3 Schiermonnikoog 84.3.1 Cover 84.3.2 Vitality and seed development 10

4.4 Comparison with 2012 and 2013 104.4.1 Cover 104.4.2 Vitality and seed development 11

5 Eilanderbalg location 11

6 Discussion 136.1 Habitat suitability 136.2 Hypothesis of seed limitation 136.3 Dispersal 14

6.3.1 Around the deployment locations 146.3.2 Origin of “new” sites. 14

6.4 Critical mass hypothesis 14

7 References 16


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1 Background

Before ca. 1930, Eelgrass (Zostera marina) was widespread throughout the whole of theWadden Sea. Infrastructural works, disease, eutrophication and other factors havecontributed to its demise. In the Dutch Wadden Sea Eelgrass has virtually disappeared.Within the European Water Framework Directive targets are set to increase its occurrence.With the reduction of nutrient runoff from land since the nineties, the area of suitable habitathas likely increased. In Germany, Eelgrass has shown a remarkable recovery in the intertidalarea. In the Netherlands this has not been the case, even though models indicate that there issuitable habitat available. A hypothesis, that the lack of recovery is due to a lack of sufficientseed availability, is currently tested in a large-scale recovery project. The methodology isbased on a technique developed in the U.S.A., where it has been successfully used,particularly on subtidal populations (Pickerell et al. 2005, Marion and Orth 2010). The methodwas adapted to be used in the intertidal in the Wadden Sea.In Van Duren et al. (2013) a full account has been presented with details of the methodology,the preliminary work, the results from the first monitoring campaign in 2012 after the firstdeployment etc. In a subsequent report the results of 2013, after the second year ofdeployment were reported (Van Duren and Van Katwijk 2013). This current report is anupdate presenting the data of the eelgrass distribution observed in 2014. This is the first yearin this project where in the previous season no active restoration efforts were carried out.

1.1 Project background

Under the water framework directive, the Netherlands is obliged to improve the habitat qualityin the Wadden Sea and implement measures that increase the population of Eelgrass (Z.marina) and of Dwarf eelgrass (Zostera noltii or Z. nana also known as Z. noltei(Rijkswaterstaat 2009). In 2010 a study was commissioned into the possibility to applyseeding techniques that have been successfully applied in the U.S. in the Wadden Sea(Erftemeijer and Van Katwijk 2010). This study established that for such a restoration effort itwould be desirable to use Eelgrass seeds from stocks from other parts of the Wadden Sea,where populations have improved significantly over the past decade. The study alsocombined the habitat suitability maps (De Jong et al. 2005) with hydrodynamic models. Thelatter were used to assess which areas with suitable habitat would have the right conditions toensure that seed-bearing shoots from an Eelgrass meadow would be retained in the area topromote next year’s crop. In spring 2011 Rijkswaterstaat, together with the environmentalsociety, the “Waddenvereniging”, assigned a project to Deltares to carry out a two-yearrestoration project, followed by a 4-year monitoring effort in an attempt to restore Z. marina tothe Wadden Sea.

1.2 Project outlineThe basic idea behind the project is to import a large amount of seed bearing eelgrass shootsfrom healthy populations in Germany, where intertidal eelgrass populations have recoverednearly to their former extent. The seed-bearing shoots are deployed in mesh bags with amesh size large enough to let the seeds fall through, but small enough to retain the grassshoots. The bags contain floats and the floats are anchored with rope to the seabed, allowingthe seeds to ripen and distribute themselves in the immediate vicinity of the deploymentlocation.The aim is to populate a large enough area with seagrass that the meadow becomes self-sustaining with respect to seed production. Using donor material from other tidal basin in the



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Wadden Sea should reduce the risk of introducing alien, invasive species. The collection ofinflorescences and the subsequent deployment takes place in the period that the seed isripening and the shoots are beginning to be released. This occurs in the German WaddenSea in the period of late August to late September. As the exact peak of seed productiondepends on weather conditions and is not predictable a long time in advance, per year twocollections were carried out – to diminish the risk of missing this peak of seed production. Asthere is in the field a large year-to-year variability in recruitment success, the collection anddeployment of seed bags have been carried out in two consecutive years. The collection ofinflorescences and the deployment of the seed bags were carried out by the FieldworkCompany and volunteers of the Wadden Vereniging, supervised by Deltares and Ecoscience.Although calculations in Erftemeijer and Van Katwijk (2010) indicate that the amount ofharvested eelgrass material should not pose any risk to the donor population, the state of thedonor populations has been monitored by a local research institute (the Alfred WegenerInstitut on Sylt). This group also carried out the effect monitoring on Sylt. The two consecutiveyears of eelgrass harvesting has not resulted in any appreciable effect on the donorpopulation (Van Duren et al. 2013).

2 Deployment locations (2011 and 2012)

Full details for the arguments supporting the location choices can be found in Van Duren etal. 2013.

2.1 UithuizenNear Uithuizen the 2011 a location site was selected 100 m long and 100 m deep (runningparallel to the saltmarsh land reclamation plots). The centre of the 2011 plot was: N53°28’02’’, E 6°41’17’’.The choice for the 2012 deployment site was just west of the 2011 site: close to the originalone and with limited chance of trampling emerging eelgrass plants. The centre of the 2012plot was: N 53°28’01.92’’, E 6°41’10.41’’ (Figure 4.1).

2.2 BalgzandThe 2011 plot at Balgzand was 250 x 40 metres and the centre was located at N 52°55’30’’and E 4°47’59”. For 2012, a deployment location slightly further south was selected. Due tolocal topography (the presence of a small gully in this area, the 2012 location was split intotwo adjacent sections, the total surface area remained 1 Ha. The centres of the tworectangles were located at: N 52°55’11.28’’, E 4°48’10.20” and N 52°55’09.05’’, E 4°48’14.18”respectively (Figure 4.4).

2.3 SchiermonnikoogThe 2011 location at Schiermonnikoog was square (100 x 100m) with the centre at N 53° 28’08’’ and E 6° 10’ 33’’.In 2012 most eelgrass appeared to the north of the 2011 location and changes appeared tohave occurred with respect to sediment composition and elevation. Based on the occurrenceof eelgrass and local bed elevation the 2012 location was situated a little closer to the dike,with the centre at N 53° 28’ 10.22’’ and E 6° 10’ 24.75’’ (Figure 4.7).



3 Data collection on Eelgrass distribution

3.1 Annual monitoring in the vicinityA comprehensive seagrass monitoring within the national monitoring framework (MWTL) iscarried out every 3 years. Specific monitoring following the same methodology is carried outannually in the immediate vicinity of the deployment sites. The first monitoring of 2012indicated that there was a bit more dispersal of seagrass around the deployment site thanwas initially expected, based on the sinking velocity of the seeds. In the 2013 monitoring thesurvey was carried out over a somewhat larger area than in 2012, taking wider marginssurrounding the deployment areas. The current 2014 survey covered the deploymentlocations and a minimum distance of 100 m surrounding the deployment locations until atleast 2 empty cells were detected at the periphery. In 2014 also the full MWTL surveycovering all Eelgrass locations in the whole Wadden Sea has taken place. This reportconcentrates on the targeted monitoring around the deployment sites and some additionalobservations at “Eilanderbalg, where in 2013 a new relatively large area with eelgrass wasobserved that likely originated from the 2011 deployment.

A full description (in Dutch) of the surveying method can be found in the RWS-CIV reports.(Bergwerff and Buiks 2012, Pranger and Tolman 2013, Tolman and Pranger 2014). The fieldwork is carried out using a grid method. Each of the three areas is divided in grid cells of20x20 m. Each area is subsequently surveyed on foot and per grid cell occurrence ofseagrass species, notably: Z. marina, Z. noltii, and Ruppia maritima are recorded on handheld computers (PDAs). The codes for the different levels of cover and the correspondingarea within a 20x20 m grid cell are given in table 1.In 2013 the monitoring was carried out byEGG consult Pranger & Tolman ecologen.This company will also carry out thesubsequent monitoring in 2015. The 2012monitoring had shown a dispersal of eelgrassat a relatively large distance from thedeployment area. In 2013 the monitoringcovered a wider perimeter around thedeployment areas, in order to be sure the fullextent of the eelgrass cover around thedeployments of both 2012 and those of 2011was covered. This was continued in the 2014monitoring.In 2013 an additional location site wasobserved where eelgrass had establisheditself, likely originating from eelgrass thatemerged after the 2011 deployment. In 2013 some extra observations were carried out to geta rough estimate of the size of the patch. This patch was revisited in 2014 (Bergwerff 2014).

3.2 Eelgrass observations reported by the public via the RWS websiteIn 2013 Eelgrass was reported by members of the public and researchers from IMARES atother locations via the RWS web-form:https://www.rijkswaterstaat.nl/formulieren/aanmeldformulier_zeegras.aspx.In 2014 no new locations have been reported.

Code Cover (%) Surface area (m2)1 >0-1 >0-42 1-5 4-203 5-10 20-404 10-20 40-805 20-30 80-1206 30-40 120-1607 40-50 160-2008 50-60 200-2409 60-70 240-28010 70-80 280-32011 80-90 320-36012 90-100 360-400

https://www.rijkswaterstaat.nl/formulieren/aanmeldformulier_zeegras.aspx



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4 Monitoring observations at deployment locations

On all three locations some eelgrass was observed in 2014, but in all cases considerably lessthan in 2013. Likely due to the extremely long protracted period of frost in spring 2013, seeddevelopment in 2013 was very late and very low. A reduced distribution and density wastherefore expected. There were however very large differences in the sizes of the remainingpopulations.The report below concentrates on the targeted monitoring around the deployment areas.

4.1 Uithuizen

4.1.1 CoverThis location was surveyed on 7, 12,13,14,16,30 and 31 July 2014.

Uithuizen2012 2013 2014

Number of surveyed cells 980 5098 624Number of cells containing Z. marina 297 2884 29Number of cells containing Z. noltii 751 not recorded 264Number of cells containing R. maritima 0 0 0

In 2014 eelgrass cover was very severely diminished at this location compared to 2013. Alsothe density within survey cells was low; the maximum number of eelgrass clumps within a gridcell was 2. The spread of eelgrass is predominantly due eastward with respect to thedeployment locations.

Figure 4.1: Surveyed area at Uithuizen. Light green patches represent 0-1% cover. The blue squares indicate theextent of the eelgrass cover in 2013. The red box indicates the deployment locations of 2012, pinkrepresents the 2011 deployment.



The Uithuizen site is characterised by a significant population of dwarf eelgrass (Z. noltii).Dwarf eelgrass prefers a slightly higher elevation, but part of the meadow consists of a mix ofZ. marina and Z. noltii. In 2013, Dwarf eelgrass had not been quantified, but in comparison tothe distribution of 2012, also the cover of this species seems to have reduced, althoughnowhere near to the same extent as Z. marina (Figure 4.2).

Figure 4.2: Surveyed areas in 2014 at Uithuizen for Dwarf eelgrass (green), compared to the distribution in 2012(purples)

4.1.2 Vitality and seed developmentAll plants looked healthy, although relatively small, 15-40 cm in length (Figure 4.3). Mostplants showed inflorescences with signs of seed development.



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Figure 4.3 A: Uithuizen, 2014, Plants looked healthy and vigorous, despite the relatively small size most showedhealthy seed development. Photo: Tolman & Pranger

4.2 BalgzandThis location was surveyed on 14, 15 and 23 August 2014. Similar to 2012 and 2013, thislocation was characterised by large amounts of macroalgae, specifically Ulva lactuca andfilamentous algae. Cover of these macro algae far outweighs the cover of Eelgrass.

4.2.1 Cover

Balgzand2012 2013 2014

Number of surveyed cells 256 981 482Number of cells containing Z. marina 118 467 97Number of cells containing Z. noltii 0 1 22Number of cells containing R. maritima 1 4 6

The distribution of eelgrass on Balgzand is shown in Figure 4.4. There are clearly two centreswith high distributions, corresponding to the deployment locations in 2012 and the one from2011. Also in this location the amount of eelgrass is distinctly smaller than in 2013, althoughthe decline is less extreme than in Uithuizen. The cover never exceeded more than 1%. Themaximum number of (clumps of) plants per grid cell was 4, but in most cases was restrictedto 1.Eelgrass did not spread much northward beyond the limits of the 2011 deployment location.The 2012 deployment location has a limited spread northward (±80m) and a 200m southwardextension.



Figure 4.4: Surveyed area on Balgzand. Light green patches represent 0-1% cover. The blue squares indicate theextent of the eelgrass cover in 2013. The red box indicates the deployment locations of 2012, pinkrepresents the 2011 deployment.

In previous years Dwarf eelgrass was seldom observed on this location. In the 2013 only oneplant was observed. This year several plants of Z. noltii were observed, all within the vicinityof the 2012 deployment area. As in previous years a few isolated plants of Ruppia maritimawere observed as well (Figure 4.5).

Figure 4.5 Locations of Dwarf eelgrass (Z. noltii, in green) and Ruppia maritima (indicated in orange) aroundBalgzand



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4.2.2 Vitality and seed developmentAs in previous years, plant vitality varied considerably on this location. Generally plants weresmaller than 40 cm in length. Mid-August many plants did show inflorescences and onset ofseed development (Figure 4.6).

Figure 4.6 On Balgzand Eelgrass often shows discoloured patches. This site is characterised by large amounts ofalgae that sometimes tend to smother the eelgrass plants. Photo: Tolman and Pranger.

4.3 SchiermonnikoogThis location was surveyed on 20 and 22 August 2014.

4.3.1 Cover

Schiermonnikoog2012 2013 2014

Number of surveyed cells 271 1620 1095Number of cells containing Z. marina 140 1077 360Number of cells containing Z. noltii 0 29 25Number of cells containing R. maritima 0 0 0

The cover of eelgrass appears to have diminished in this location, but to a somewhat lesserextent than Uithuizen and Balgzand. During the 2013 survey, a substantial amount of plants



was observed relatively close to the dyke, an area that was not surveyed in 2012. Also in2014 eelgrass cover extends all the way to the dyke. The extension eastward is distinctly lessthan it was in 2013. South of the deployment the spread was limited.Densities were also marginally higher here than at the other two sites. Maximum number ofplants observed per grid cell was 13, although in most locations it was just one or two plants.

Figure 4.7: Surveyed area on Schiermonnikoog. Light green patches represent 0-1% cover. The blue squaresindicate the extent of the eelgrass cover in 2013. The red box indicates the deployment locations of 2012,pink represents the 2011 deployment.

In 2013 29 cells were observed to contain Z. noltii, all these cells were within the 2012deployment perimeter. In previous years this species has not been observed atSchiermonnikoog, and it is virtually certain that these plants originate from dwarf eelgrass atSylt, as the donor location is a mixed meadow.Also in 2014 this species was observed, partly in the same location as in 2013, but curiouslythis year also within the perimeter of the 2011 deployment, where no dwarf eelgrass wasobserved previously (Figure 4.8).



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Figure 4.8 Distribution of dwarf eelgrass on Schiermonnikoog in 2014

4.3.2 Vitality and seed developmentAll plants at this location appeared healthy, the smallest plants measured around 20 cm andthe largest ones 60 cm. Although not quantified it appears that plants are slightly smaller thanin previous years, when maximum sizes of up to 80 cm in length were reported. Nearly allplants showed development of seed in inflorescences.

4.4 Comparison with 2012 and 2013

4.4.1 CoverDespite the fact that in 2012 not the full extent of the eelgrass distribution was covered by thesurvey, it is very clear that in 2013, in all three locations eelgrass cover extended, while in2014 the populations retreated. A comparison has been made between the cells that weresurveyed in all three years (Figure 4.9).



Figure 4.9: Comparison between 2012, 2013 and 2014 in terms of proportion of cells containing eelgrass; 100%being the total number of cells surveyed in 2012, 2013 and 2014, n = the number of cells surveyed in allthree years.

Figure 4.9 shows the development over the 3 years, indicating that the cover in 2013 wasless patchy than in 2012 and 2014. The decline at the Uithuizen site is the most extreme. Inprevious years, this site showed the largest extension of eelgrass. At all three sites thevegetation appeared to be also more patchy than it was after the first deployment in 2012,although slightly less distinct at Schiermonnikoog.

4.4.2 Vitality and seed developmentIn all three years most plants appeared predominantly healthy and vigorous. Balgzand is a bitof an exception as it tends to have a relatively high proportion of plants with discolourations,almost certainly due to the large amount of decaying algae at this site. There was noindication that the condition of the leaves differed between years, although plant sizes appearto be smaller in 2014 compared to previous years.Although seed development was never quantified, all observations indicate that seeddevelopment in 2013 was conspicuously later and also less than in the previous year. Thereseemed to be relatively few male inflorescences at all sites in 2013. In 2014, despite therelatively small size of the plants seed development was (on the face of it) similar to 2012.

5 Eilanderbalg location

After receiving a notification of several Z. marina plants near buoy EB7 at Eilanderbalg in2013, employees of RWS CIV (formerly DID) decided to carry out a preliminary inventory, inorder to assess whether this location ought to be taken up in the regular monitoring program.In 2014 this site was revisited on 2 days (4 and 5 August). The first day a similar route to



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2013 was covered, although the small isolated patch that was found in 2013 was notrevisited. On day 2 the site was approached from the Schiermonnikoog direction and an areawas surveyed that was not visited the previous year.

Figure 5.1: Detail of the surveyed area in 2014 with the cyan coloured points indicating the presence of eelgrassplants. Red circles indicate the location of eelgrass in 2013.

In total 3689 cells were surveyed, of which 25 contained eelgrass plants. The distancebetween the plants in this area was large and this site does not constitute a coherentmeadow, like it appeared to be in 2013.

The plants appeared healthy, with dense leaves, and nearly all plants showed seeddevelopment (Figure 5.2). Most plants ranged around 20-30 cm, while the largest onesreached up to 60 cm. This appeared to be smaller than the plants that were observed in2013. Some seed development was observed.



Figure 5.2 Plants with inflorescences at EB7 buoy, photo RWS-CIV

6 Discussion

6.1 Habitat suitabilityFrom results of the previous years it was already clear that the “Habitatkansenkaart” is avaluable instrument in selecting suitable areas and that there is indeed a reasonable amountof suitable habitat available in the Wadden Sea. At the very small scale accurate prediction ofmaximum suitability is slightly more difficult. The Wadden Sea is a dynamic area and exactlocations with the right elevation, the right wave exposure etc. will shift from year to year. InUithuizen and Balgzand most of the spread of the eelgrass is parallel to the coast, indicatingthat elevation is restrictive for the distribution of this species, very likely due to limitations inlight availability. On Schiermonnikoog, the first year the location of the deployment area wasselected on the basis of detailed local elevation maps. The subsequent years showed adistinct spread towards the dyke, with seagrass growing right to the “toe” of the dyke. At thislocation a small mussel bed on the seaward side of the deployment area disappeared after anautumn storm in 2011. Whether small scale elevation subsequently changed was notchecked.

6.2 Hypothesis of seed limitationThis project was started on the basis of the hypothesis that there is currently in the WaddenSea much more suitable habitat for Eelgrass than the distribution in 2010 showed. Thereason for the lack of recovery in the Netherlands compared to the German Wadden Sea was



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assumed to be limitation of seed availability, as the intertidal variety of Z. marina for the mostpart has to regrow from seed every year. In 2013 all (qualitative) observations indicated thatseed development that year was severely inhibited. Although the plants appeared healthy andlarge, seed developed very late, there appeared to be a distinctly skewed male-female ratio(very few male flowers were observed) and very few plants appeared to have produced viableseeds in late summer (Van Duren and Van Katwijk 2013). The poor development of eelgrassin 2014 after a year with very poor seed development is a very strong indication that seedlimitation is indeed the most likely cause of the limited level of recovery of eelgrass in theWadden Sea at present.

6.3 Dispersal

6.3.1 Around the deployment locationsThe fact that the original Balgzand deployment locations of 2011 are still recognisable in thefield, separated from the 2012 location, indicates that a substantial proportion of the producedseeds germinates very locally and hardly disperses at all. This was also observed in 2013.This is in terms of a restoration technique very promising. On one hand, the aim of theexercise is of course for the created eelgrass meadows to act as a source population forfurther dispersal. On the other hand, good local retention assures that also the original sitewill be repopulated the subsequent year.

6.3.2 Origin of “new” sites.Based on the original dispersal models the most likely origin for the Eilanderbalg site wasdeemed to be Uithuizen, although it is theoretically possible that seeds originated from theSchiermonnikoog location, which is as the crow flies closer, but is on the other side of thetidal divide. Recent fine sediment models have indicated that the transport of very finesediment across tidal divides is more substantial than previously thought, however whetherthe relatively large inflorescences are easily transported over the shallow intertidal areasremains to be seen. Bed-load transport of the heavy and large seeds over so manykilometres (i.e. transport of seeds that are buried within the sediment) seems unlikely.In 2014 no observations were made at Rottum and no other distinctive sites were reported.

6.4 Critical mass hypothesisThe other main hypothesis that this project is testing is that in order to ensure long-termsurvival of Eelgrass any restoration effort needs to be large-scale. Recruitment varies stronglyyear-to-year. A restoration site needs to be large enough to survive a few successive ‘bad’years. It will take several years to assess whether the effort from the current project has beenlarge enough to create sufficient critical mass.In 2013 no new seed bags were deployed in the Wadden Sea. It currently looks like the coldspring has caused limited recruitment in 2014. Certainly at Uithuizen the left-over populationdoes not appear to be viable.

The initial success of this project has received a lot of attention and there are a number ofinitiatives and ideas among NGOs and managing authorities (national and local) to expandthe restoration effort to other areas. In 2014 a consortium of NGOs has received a grant fromthe “Waddenfonds” for additional restoration efforts in the vicinity of the current deployments.Their 2014 deployments coincided with the 2012 deployment sites for Balgzand andUithuizen, while on Schiermonnikoog the location is in the 2011 deployment site (Figure 6.1).



The results of 2012indicate that even afterone year there can be afair bit of dispersal of seedaround deployment areas(on Schiermonnikoogeelgrass was observed ata distance of up to 600 mfrom the deployment site).Next year it will thereforebe not be possible todifferentiate betweenplants originating from the2011 and 2012deployments and the2014 deployment, at leastat the Schiermonnikoogsite. At the Uithuizen sitethe number of plants leftis so low that thecontribution of theprevious deployments willbe minimal. Only atBalgzand the 2011 sitemay remaindistinguishable from the2014 site, as these siteshave been spatiallyseparated.

Figure 6.1 Locations of the 2014 deployments of the Waddenfondsproject in relation to the 2011 and 2012 deployment sites and the2014 distribution of eelgrass. Note that the boundaries of the2012 and 2014 deployments at Uithuizen overlap virtuallycompletely, leaving the 2014 marking obscured.



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7 References

Bergwerff, J. W. 2014. Verslag bezoek locatie Eilander Balg (Boei EB7) 2014. RWS-CIV.Bergwerff, J. W. and J. Buiks. 2012. Monitoring Herstel Groot Zeegras Waddenzee 2012. RWS -

Data-ICT-Dienst.Erftemeijer, P. L. A. and M. M. Van Katwijk. 2010. Zeegrasproef Waddenzee. Grootschalig

zeegrasherstel in de Nederlandse Waddenzee door middel van zaadverspreiding.Deltares, Delft.

Marion, S. R. and R. J. Orth. 2010. Innovative techniques for large-scale seagrass restorationusing Zostera marina (eelgrass) Seeds. Restoration Ecology 18:514-526.

Pickerell, C. H., S. Schott, and S. Wyllie-Echeverria. 2005. Buoy-deployed seeding:Demonstration of a new eelgrass (Zostera marina L.) planting method. EcologicalEngineering 25:127-136.

Pranger, D. P. and M. E. Tolman. 2013. Monitoring Herstel Groot zeegras Waddenzee 2013.BM13.22, Rijkswaterstaat CIV, Delft.

Rijkswaterstaat. 2009. Programma Rijkswateren 2010-2015, Uitwerking Waterbeheer 21e eeuw,Kaderrichtlijn Water en Natura 2000. Rijkswaterstaat, Lelystad.

Tolman, M. E. and D. P. Pranger. 2014. Monitoring Herstel Groot zeegras Waddenzee 2014.BM14.19, EFTAS Fernerkundung Technologietransfer GmbH.

Van Duren, L. A. and M. M. Van Katwijk. 2013. Eelgrass restoration in the Dutch Wadden Sea,Results 2013. 1203892-000-ZKS-0040, Deltares, Delft.

Van Duren, L. A., M. M. Van Katwijk, J. Heusinkveld, and K. Reise. 2013. Eelgrass restoration inthe Dutch Wadden Sea; Methodology and first results. 1203892-000-ZKS-0033, Deltares.

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